Computed Tomography-Based Morphometric Analysis of the Ascending Aorta in Acute Type A Dissection Beyond Diameter-Based Thresholds: A National Cohort Study from Latvia

Background/Objectives: Ascending aortic aneurysm is a heterogeneous disease, with many cases of acute Stanford type A aortic dissection (ATAAD) presenting with aortic diameters below currently recommended surgical thresholds. Demographic factors such as age and sex, along with indexed aortic size groups, have been proposed to improve risk stratification. Methods: We included 65 adult patients who underwent surgical intervention for ATAAD. Morphometric measurements were obtained from computed tomography angiography (CTA) using centerline reconstruction. Maximum ascending aortic diameter and length were measured. Indexed parameters included the aortic size index (ASI), aortic height index (AHI), aortic length index (ALI) and cross-sectional aortic area indexed to height (CSA/H). Estimated pre-dissection dimensions were derived by reducing diameter by 18% and length by 2.7%. The cohort was stratified by age-, sex-, and ASI-defined groups. Results: Women were older than men (mean age 67 [SD 11] vs. 58 [SD 13] years, p = 0.01). Aortic diameter and length did not differ significantly by age or sex. At presentation, an ascending aortic diameter < 5.0 cm was observed in 37.1% of patients aged < 65 years and 26.7% of those aged ≥ 65 years. When stratified by sex, 25.0% of women and 35.6% of men presented with an ascending aortic diameter < 5.0 cm. Indexed parameters (ALI, AHI and ASI) were higher in older patients and women despite their smaller body size. In estimated pre-dissection analyses, less than 10% of the patients had diameters ≥ 5.5 cm, whereas most had estimated diameters < 5.0 cm. Conclusions: A substantial proportion of patients with ATAAD present with aortic dimensions below the current surgical thresholds. These findings underscore the limitations of diameter-based criteria and support the potential value of indexed geometric parameters in improving risk assessment in ATAAD patients.